This invention relates to a two cycle engine and more particularly to a direct cylinder injection method and control strategy for such engine.
It is well known that the simplicity of two cycle engines and their ability to produce greater power output for a given displacement than four cycle engines presents a number of advantages, particularly in certain types of applications. However, the exhaust emission control situation with two cycle engines has placed pressure on many manufacturers to convert to four cycle engines for applications normally enjoyed by two cycle engines.
One area where two cycle engines are widely used is in conjunction with outboard motors. With an outboard motor, the engine is, however, required to run over a wide variety of speed and load ranges. For example, it is not untypical for an outboard motor to be operated either at full throttle, full power or in a trolling condition. In this latter condition, the engine actually runs at lower than idle speed. This is a particularly difficult area for two cycle engines to operate in efficiently, particularly when they are designed to produce high power outputs at full throttle.
In order to maintain the desired idle speed and fuel economy and for other reasons, it has been the practice to operate two cycle engines under some conditions with a so-called cylinder skipping method. This methodology is particularly employed when there is some difficulty with the engine or other malfunction that requires the operator to be able to be able to reach port safely, but still protect the engine from damage.
In this limp hold mode, cylinder disabling is frequently employed. This is done by skipping the firing of the cylinders for one or more revolutions. The number of cylinders skipped also varies depending upon the engine speed control that is desired.
The conditions when cylinder skipping is employed may be when shifting the transmission, when there is a danger of decrease in oil availability or when the engine is operating at a high temperature or high speed.
When the cylinder skipping is employed, fuel continues to be supplied to the engine. This is done because of the difficulty in transitioning the operation from skipping mode back to full cylinder operation mode. This is particularly necessary where the charge is delivered to the engine through the crankcase chamber and scavenge arrangement. It takes some time for the fuel charge to reach the combustion chamber and thus it may be necessary to supply fuel even when the cylinder is not being operated. This obviously adds to the emission problems.
There has been proposed, therefore, a system for direct cylinder injection in two cycle engines. However, the injection timing employed with conventional direct injected two cycle engines also can present some emission and smooth running problems. Therefore, a system has been proposed by us that is described in the co-pending application entitled, "Control for Direct Injected Two Cycle Engine", Ser. No. 09/188953, Filed Nov. 10, 1998 and assigned to the Assignee hereof, where the injection initiation and duration is controlled so as to minimize the likelihood of fuel escaping from the exhaust port while still obtaining maximum power output. In accordance with that arrangement, the initial fuel injection is begun at a point when the exhaust port is still open but at a time wherein the fuel injected will not reach the exhaust port during the time when the exhaust port is still open. Basically, injection is done while the exhaust port is open rather than delaying it until after it closes as with more conventional methodologies.
It is an object of this invention to take advantage of that methodology and to also enable the engine to operate with speed control that may require cylinder skipping, but which will reduce the likelihood of the exhaust gases containing unburned hydrocarbons.
It is a further object of this invention to provide a direct cylinder injected two cycle engine having a control arrangement wherein engine speed reduction is obtained with cylinder skipping but which improves transition to that mode and also back to normal running and also to avoid the discharge of hydrocarbons to the atmosphere.
It is a further object of this invention to provide an improved method and construction for providing reduced engine speeds in direct injection two cycle engines under some running conditions without adversely affecting engine emission control or transitioning to that condition and transition from that condition back to normal running.